Composite materials

ABSTRACT

A composite material is formed by combining an expandable polymer having a charge with another polymer having an opposite charge to produce. In particular, the composite material can be prepared by combining the polymers with a medium such as and water, and expanding the mixture using a treatment that expands the mixture to produce, for example, insoluble porous foam-like composites.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.61/772,716 filed Mar. 5, 2013 the entire disclosure of which is herebyincorporated by reference herein.

TECHNICAL FIELD

The present disclosure relates to an insoluble porous foam-likecomposite material which can be formed by combining an expandablehydrophilic polymer with an oppositely charged hydrophilic polymer. Inparticular, the composite material can be prepared by combining thepolymers with a polar medium, such as water, and expanding the mixtureusing a thermal treatment.

BACKGROUND

Insoluble low density, porous materials such as foams are needed for awide variety of commercial applications including insulation materials,packaging materials, absorbent materials for applications ranging frompersonal hygiene to liquid hazardous waste remediation or removal,porous materials for biomedical applications including wound care andtissue regeneration, and, if edible, materials for food production suchas ‘puffed’ food products or diet food products. Furthermore, materialswhich are compostable offer improved sustainability as they can bedisposed safely in land fills or even used as an energy source throughprocesses such as anaerobic digestion.

Starch, a natural biopolymer found in plants such as corn or potato, hasbeen extensively utilized to develop expandable or so-called ‘puffed’materials with other ingredients. Glenn et al. (U.S. Pat. No. 5,958,589,1995) developed a starch-based microcellular foam using a novel solventexchange method, and they claimed that such a material had superiorproperties such as improved mechanical strength, high pore volume, andlow density. A starch-lignin foam was prepared by Stevens et al.(Stevens, E. S., Klamczynski, A., and Glenn, G. M. 2010. Starch-ligninFoams. Express Polymer Letters 4 (5): 311-320), which showed that a 20%replacement of starch with lignin had no adverse effect on foam densityand morphology. More recently, Dougherty et al. (U.S. patent application#2010/0189843, 2010) described a hydroxypropylated starch to improve theextrusion process of a food composite whereby the hydroxypropylatedstarch aids in the retention of dietary fiber contained in thecomposite. Also, other biopolymers such as carboxymethyl cellulose andxanthum gum have been applied to expand with starch, which is said toimprove the shape, texture and structure of starch-based composite. SeeGimeno, E., Moraru, C. I., and Kokini, J. L. 2004. Effect of Xanthan Gumand CMC on the Structure and Texture of Corn Flour Pellets Expanded byMicrowave Heating. Cereal Chemistry 81 (1): 100-107. Starch has alsobeen used as an adhesive for the production of corrugated cardboard. SeeOnusseit, H. 1992. Starch in industrial adhesives: new developments.Industrial Crops and Products. 1(2-4):141-146. Starch composites whichconsist of principally biologically derived polymers, however, aretypically soluble in polar solutions, limiting their use in manyapplications. Thus, a need exists to create insoluble composites such asinsoluble starch composite with high liquid absorbing capability.

SUMMARY OF THE DISCLOSURE

An advantage of the present invention is a composite material that canbe used for a variety of applications. Advantageously, the composite isinsoluble in liquid environments and capable of absorbing many times itsown weight. The composite can also be used as an adhesive.

These and other advantages are satisfied, at least in part, by acomposite material such as a foam-like porous material composition whichis insoluble in liquid environments. Advantageously the compositematerial is capable of absorbing many times it s own weight, e.g., asmuch as about 11 times its weight, in liquid and over a wide pH range,e.g., a pH range of about 2-12.

Embodiments of the present invention include an insoluble low densityporous composite material containing at least one polymer having acharge, e.g., an anionic starch, and at least one polymer of oppositecharge, e.g., cationic polysaccharide such as chitosan.

Another aspect of the present disclosure includes a process of preparinga composite material. The process comprises mixing at least one solublepolymer having a charge, e.g., at least one anionic polymer, at leastone soluble polymer of opposite charge, e.g., at least one cationicpolymer, and at least one polar solvent, e.g., water. Advantageously, atleast one of the soluble polymers in the mixture is capable ofexpanding. The mixture is then expanded by one or more techniques thatare known to expand at least one expandable polymer. Such techniquesinclude, for example, thermal treatment, e.g., such as where thetemperature of the treatment exceeds about 100 degrees Celsius, thermalextrusion, a microwave treatment, etc.

Additional embodiments include wherein the anionic starch is notgelatinized, the anionic starch contains at least 75% w/w amylopectin,the anionic starch is in an amount of at least 75% w/w and theoppositely charged polymer, e.g., a cationic polysaccharide, is between2% w/w and 10% w/w, the polar solvent or the water is in an amountbetween 40% w/w and 80% w/w water in the mixture. The composites canalso advantageously include other additives such as between 1% w/w and25% w/w cellulose or nanocellulose, between 0.01% w/w to 1% w/wpolyhexamethylene biguanid, antimicrobial agents, such as between 1% and5% of sodium benzoate, etc. The present disclosure also contemplates thecomposites made by the processes described herein.

Additional advantages of the present invention will become readilyapparent to those skilled in this art from the following detaileddescription, wherein only the preferred embodiment of the invention isshown and described, simply by way of illustration of the best modecontemplated of carrying out the invention. As will be realized, theinvention is capable of other and different embodiments, and its severaldetails are capable of modifications in various obvious respects, allwithout departing from the invention. Accordingly, the drawings anddescription are to be regarded as illustrative in nature, and not asrestrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 provides three graphs showing the determination of swelling ratio(water uptake in % w/w of water to dry composite) of starch-chitosancomposites swollen in solutions with different pH values according toembodiments of the present disclosure. FIG. 1( a) shows the swellingratio with a pH 2, FIG. 1( b) shows the swelling ratio with a pH 7 andFIG. 1( c) shows the swelling ratio with a pH 12.

DETAILED DESCRIPTION OF THE DISCLOSURE

The present disclosure relates to composite materials that are insolublein liquid environments but can absorb a large amount of liquid. Thecomposite materials of the present disclosure can advantageously absorba liquid in an amount that is many times its own weight, e.g., as muchas about 11 times its weight, and over a wide pH range, e.g., a pH rangeof about 2-12. Other advantages of the composites of the presentdisclosure include a very simple production process. In addition some ofthe composites can be fabricated to yield completely compostablematerials when produced using natural biologically derived polymers. Thecomposites can also be formed or molded into a wide variety of shapes,including a process where the hydrated material is dehydrated within amold where it can expand during dehydration to fill the mold and takethe shape of the mold. In an aspect of the present disclosure, the moldwould have some pores to allow water vapor to escape. Composites of thepresent disclosure include, for example, insoluble low densitycomposites such as highly porous foams containing at least one polymerhaving a charge, e.g., an anionic starch, and at least one polymer ofopposite charge, e.g., cationic polysaccharide such as chitosan.

The composites can be prepared by mixing at least one soluble polymerhaving a charge, at least one soluble polymer of opposite charge, and atleast one polar solvent, wherein at least one of the soluble polymers iscapable of expanding. The mixture is then expanded.

Soluble polymers useful for the present disclosure include, for example,polymers that are soluble in the polar solvent and carrying either anegative or positive charge. Such polymers having a charge includeanionic polymers, such as, for example, at least one anionic starch,alginic acid, pectin, xanthan gum, hyaluronic acid, chondroitin sulfate,keratin sulfate, gum arabic, gum karaya, gum tragacanth, heparin,chondroitin, polyacrylic acid and it's derivatives, many proteins suchas the caseins.

Soluble polymers of opposite charge, e.g., cationic polymers, that aresoluble in the polar solvent include, for example, at least one cationicpolysaccharide such as chitosan, cationic guar gum, cationichydroxyethylcellulose, cationic starch, cationic cellulose, pectin, andcationic polyethylene glycol.

Polar solvents useful for solubilizing the polymers include, forexample, water, aqueous solvents including ethylene or propylene glycol,alkyl lactate, and optionally alcohol or organic carbonates, loweralcohols such as methanol, ethanol, n-propanol and isopropanol.

It is believed that the polymers while soluble in the polar solvent whenforming the mixture become insoluble upon expansion because the cationicpolymer electrostatically crosslinks with the anionic polymer during theexpansion process where the polymers can interact.

In one aspect of the present disclosure, the process of preparing thecomposite material includes preparing a mixture containing (i) at leastone anionic starch as the at least one soluble polymer having a charge,(ii) at least one cationic polysaccharide as the at least one solublepolymer of opposite charge, and (iii) at least one polar solvent, e.g.water. The mixture is then expanded by one ore more techniques that areknown to expand the at least one expandable polymers. Such techniquesinclude, for example, thermal treatment, e.g., such as where thetemperature of the treatment exceeds about 100 degrees Celsius, thermalextrusion, a microwave treatment, etc. Starch, for example, especiallyamylopectin, is well known to exhibit extensive expansion capacity underthermal processing, including microwave heating and thermal extrusion.Expanded starch, however, is readily soluble in aqueous solutions.

An expandable soluble polymer such as an anionic starch can be combinedwith a cationic polymer such as chitosan and water to expand the mixturethrough microwave processing or other thermal treatments such as thermalextrusion. The anionic starch can be an anionic amylopectin or a starchwhich contains phosphate such as many starches derived from potato(where the starch contains one phosphate ester group per approximately40 to 400 anhydroglucose units). The cationic polymer can also be acationic guar or cationic starch.

It is preferable to use a starch which has not been gelatinized toimprove the characteristics of the expanded composite including thedegree of expansion during thermal treatment which would result in alower density insoluble composite.

For example, an expanded insoluble composite can be produced using thefollowing process. Chitosan solution was prepared by mixing chitosan(Sigma-Aldrich, Saint Louis, Mo.) in 1% (v/v) formic acid andmagnetically stirred at 600 rpm for 24 hours under room temperature. ThepH of the chitosan solutions ranged from 4 to 5; the preferred pH is4.5. The contents of chitosan in the above solutions ranged from 1.67%to 5% (w/v), preferably at about 5% (w/v). After the chitosan wasdissolved and the solution became clear, the solution was poured into acontainer for further mixing with potato starch (MP Biomedicals, Solon,Ohio).

Starch-based chitosan composite foams were prepared as follows. 2.7 mlchitosan solutions with different concentrations ranged from 1.67% to 5%(w/v) were added to 1.8 gram non-gelatinized potato starch powder(containing at least 50-75% amylopectin). The final weight ratios ofchitosan to potato starch were from 2.5% to 7.5% (w/w), where ratio of7.5% was most desired. The starch-chitosan mixtures were then stirred at250 rpm for about 2 minutes. After blending, the mixtures were heated bymicrowave at 100% power of 900 W at 2450 MHz for 35-50 seconds.

FIG. 1 shows the swelling ratio (water uptake in % w/w of water to drycomposite) of varied starch-chitosan composites prepared by microwavetreatment. Swelling behavior was examined at three different pH values:2, 7 and 12. It is shown in FIG. 1 that all composites can be immersedin acidic (pH2), neutral (pH7) and basic (pH12) environment and remaininsoluble for as long as 120 hours. The swelling equilibriums fordifferent starch composites are different depending on specific pHenvironment. Specifically, composites immersed in pH 2 and pH 12 reachedequilibrium faster than that at pH 7. At pH 2 and pH 12, the equilibriumwas achieved after immersion for 8 hours, whereas at pH 7 it took 24hours to achieve equilibrium. Generally speaking, the higher thechitosan content in the composite, the better the swelling ratio will bein solution, except the case at pH12. At pH 2, the maximum values ofswelling ratio for 2.5%, 5% and 7.5% starch-chitosan composite were746%, 896% and 1137%, respectively. Likewise, at pH7 the maximumswelling ratios for 2.5%, 5% and 7.5% starch-chitosan composite were698%, 896% and 1035%, respectively. However, such a behavior did notexist at pH12 where swelling ratios for all composites showed nosignificant difference, and the maximum swelling ratio reached around613% for all composites after equilibrium. Furthermore, compositesimmersed in lower pH behave better than those immersed in higher pH interms of swelling ratio. Take 7.5% starch-chitosan composite, forexample, the maximum swelling ratios at pH2, pH7 and pH12 were 1137%,1035% and 613%, respectively. Such a performance can be seen in 2.5% and5% starch-chitosan composites as well.

Other additives can also be included in the composite. For example,cellulose or other insoluble polymer fiber can be added to modify themechanical properties of the composites. Specifically,starch:chitosan:cellulose composites can be created with modifiedproperties where the component ratios can range from approximately50-80% starch, 2-10% chitosan, and 10-48% cellulose. To reducebrittleness, approximately 1% to 25% of glycerol can be added w/wrelative to the total dry weight of all composite components. Glycerolcan be added and mixed into the solution before microwave, thermalextrusion, or other thermal processing. Other additives are alsopossible including but not limited to polyethylene glycol, poly lacticacid, or poly lactic glycolic acid. Final hydration levels beforethermal processing can range from approximately 40% to 80% where 60% ispreferred. Other component additives may be more suitable for specificapplications. For example, collagen may provide a benefit for biomedicalapplications. In addition, various additives such as antimicrobial andtherapeutic agents can be added before or after microwave processing.Therapeutic agents include compounds such as polyhexamethylene biguanide(PHMB), sodium benzoate, or any contained in U.S. Patent Application20110150972, 2011. If added as a solution after microwave processing bysoaking the composite in solution or spraying a solution onto thecomposite, the composite can be subsequently dehydrated by freeze dryingto permit long term storage. The use of chitosan in the composite mayprovide some measure of natural antimicrobial properties.

Insoluble expanded or non-expanded starch composites as described aboveusing other production techniques can also be employed to prepare thecomposite. These production techniques include various extrusion,molding and electrospinning techniques, both of which are well known tothose skilled in the art. Electrospinning of starch based materials iswell known and often involves solvents other than water such as, forexample, ethanol. The use of other polar solvents other than water isacceptable in the formation of any of the composites described herein.

As disclosed herein, improvements to extruded and electrospun materialcan be achieved by adding cellulose and glycerol. In the case ofmaterials with dimensions less than 1 mm, nanocellulose, cellulosenanofibers, cellulose nanocrystals or cellulose nanowhiskers can be usedas the cellulose material. These forms of cellulose are cellulosematerials which exhibit at least one dimension less than about 100 nm.

EXAMPLES

The following examples are intended to further illustrate certainpreferred embodiments of the invention and are not limiting in nature.Those skilled in the art will recognize, or be able to ascertain, usingno more than routine experimentation, numerous equivalents to thespecific substances and procedures described herein.

Starch-chitosan composite foams were prepared as follows. Chitosansolutions were prepared with different concentrations ranging from 1.67%to 5% (w/v) by mixing chitosan (available from Sigma Aldrich, SaintLouis, Mo.) having a molecular weight between approximately 2 kDa and100 kDa, where higher molecular weights may be preferred, includingthose in excess of 100 kDa, in an acidic solution where formic acid wasadded to DI water to a pH between 4 and 5, preferably 4.5 where thefinal concentration of chitosan ranged from approximately 1.67% to 5%(w/v), preferably at about 5% (w/v). Then 2.7 ml of the chitosansolution was added to 1.8 grams of non-gelatinized potato starch powder(containing at least 50-75% amylopectin) (available from MP Biomedicals,Solon, Ohio). The final weight ratios of chitosan to potato starch werefrom 2.5% to 7.5% (w/w). A final weight ratio of chitosan to potatostarch of 7.5% was most desired to produce a composite which exhibitedthe most water absorption capacity and which was the most stable whensubmerged for prolonged periods (approximately 5 days) in highly acidic(pH 2) or highly basic (pH 12) solutions. The starch-chitosan mixtureswere then stirred at 250 rpm for about 2 minutes. After blending, themixtures were heated by microwave at 100% power of 900 W at 2450 MHz for35-50 seconds. During the microwave treatment water is converted towater vapor and the starch gelatinizes in the presence of the chitosan.The generation of water vapor causes the viscous starch-chitosan mixtureto expand until dehydrated. During this process, the cationic chitosanbinds with the anionic starch creating an insoluble composite.

While the claimed invention has been described in detail and withreference to specific embodiments thereof, it will be apparent to one ofordinary skill in the art that various changes and modifications can bemade to the claimed invention without departing from the spirit andscope thereof. Thus, for example, those skilled in the art willrecognize, or be able to ascertain, using no more than routineexperimentation, numerous equivalents to the specific substances andprocedures described herein. Such equivalents are considered to bewithin the scope of this invention, and are covered by the followingclaims.

What is claimed is:
 1. A process of preparing a composite material, theprocess comprising mixing at least one soluble polymer having a charge,at least one soluble polymer of opposite charge, and at least one polarsolvent, wherein at least one of the soluble polymers is capable ofexpanding; and expanding the mixture.
 2. The process of preparing acomposite material according to claim 1, the process comprisingpreparing a mixture containing (i) at least one anionic starch as the atleast one soluble polymer having a charge, (ii) at least one cationicpolysaccharide as the at least one soluble polymer of opposite charge,and (iii) water as the at least one polar solvent and subjecting themixture to a thermal treatment.
 3. The process of preparing a compositematerial according to claim 1, the process comprising preparing amixture containing (i) at least one anionic starch as the at least onesoluble polymer having a charge, (ii) at least one cationicpolysaccharide as the at least one soluble polymer of opposite charge,and (iii) water as the at least one polar solvent and subjecting themixture to a microwave treatment.
 4. The process of preparing acomposite material according to claim 1, the process comprisingpreparing a mixture containing (i) at least one anionic starch as the atleast one soluble polymer having a charge, (ii) at least one cationicpolysaccharide as the at least one soluble polymer of opposite charge,and (iii) water as the at least one polar solvent and subjecting themixture to a thermal extrusion.
 5. The process of preparing a compositematerial according to claim 1, the process comprising preparing amixture containing (i) at least one anionic starch as the at least onesoluble polymer having a charge, (ii) at least one cationicpolysaccharide as the at least one soluble polymer of opposite charge,and (iii) water as the at least one polar solvent and forming a fiber ofthe composition using electrospinning.
 6. The process of claim 1, theprocess comprising preparing a mixture containing (i) at least oneanionic starch as the at least one soluble polymer having a charge, (ii)at least one cationic polysaccharide as the at least one soluble polymerof opposite charge, and (iii) at least one polar solvent, wherein theanionic starch contains at least 75% w/w amylopectin.
 7. The process ofclaim 1, the process comprising preparing a mixture containing (i) atleast one anionic starch as the at least one soluble polymer having acharge, (ii) at least one cationic polysaccharide as the at least onesoluble polymer of opposite charge, and (iii) at least one polarsolvent, wherein the anionic starch is not gelatinized.
 8. The processof claim 1, the process comprising preparing a mixture containing (i) atleast one anionic starch as the at least one soluble polymer having acharge, (ii) at least one cationic polysaccharide as the at least onesoluble polymer of opposite charge, and (iii) at least one polarsolvent, wherein the anionic starch is in an amount of at least 75% andthe cationic polysaccharide is between 2% and 10%.
 9. The process ofclaim 1, wherein the polar solvent is in an amount between 40% and 80%in the mixture.
 10. The process of claim 1, wherein the mixture furthercontains between 1% and 25% cellulose.
 11. The process of claim 1,wherein the mixture further contains between 1% and 25% nanocellulose.12. The process of claim 1, wherein the mixture further contains between0.01% to 1% polyhexamethylene biguanid.
 13. The composite preparedaccording to claim
 1. 14. The composite prepared according to claim 6.15. The composite prepared according to claim
 7. 16. The compositeprepared according to claim
 8. 17. The composite prepared according toclaim
 9. 18. The composite prepared by claim
 10. 19. The compositeprepared by claim
 11. 20. The composite prepared by claim 12.